The present invention relates generally to Code Division Multiple Access (CDMA) communication systems, and more particularly, to a system and method for integrating a priority-based quality of service in CDMA communication systems that implement data packet transmission, in order to effectively allocate radio resources.
Future mobile cellular networks must be able to support data communication, particularly packet data communications. One question that is raised is how the radio resources are to be allocated in a system that transports data packets over the radio interface in an asynchronous manner. For example, where a mobile terminal transmits and receives internet protocol (IP) data packets, the radio resource may be used without any predictable pattern. Therefore, it would be beneficial to have a system and method that effectively allocates radio resources among different connections. One radio communications scheme that could provide such a radio interface for data communications is CDMA. The present invention describes various manners in which data packets can be communicated via a CDMA communications system, such that congestion problems can be effectively managed.
In order to fully appreciate the concept, purpose, and advantages of the present invention, a general understanding of Code Division Multiple Access (CDMA) radio technology is necessary. CDMA technology is fundamentally based on spread spectrum modulation. Generally, spread spectrum modulation is a type of modulation that scatters data transmissions across an available frequency band in a pseudorandom pattern. Spreading the data across the frequency spectrum causes the signal to be more resistant to noise, and has a high tolerance to jamming and signal interception.
A spread spectrum signal is one that is transformed with a function e(c) using a code c. The code, typically a pseudo-random code, is a sequence that is combined with the data signal to transform the initial narrowband signal into a wideband signal that can have the appearance of a noise signal. The effect of this transformation is illustrated in FIG. 1, which includes FIGS. 1A, 1B and 1C.
Referring first to FIG. 1A, a narrowband signal Sn 10a is shown in the frequency domain having a bandwidth Bn. The signal Sn 10a is transformed by the function e(c) using a code c to produce the wideband signal Sw 10b having bandwidth Bw as shown in FIG. 1B. To create the wideband signal Sw, the narrowband signal Sn is xe2x80x9cspread outxe2x80x9d using the function e(c) over the increased bandwidth Bw, typically using a spreading technique such as direct sequence (DS) or frequency hopping (FH). These spreading techniques are well-known in the art. The wideband signal Sw 10b is then transmitted, and the targeted receiver applies the same function e(c) based on code c to the transmitted wideband signal Sw 10b to reproduce the initial narrowband signal Sn 10c, as shown in FIG. 1C.
The term Code Division Multiple Access indicates that there can be several signals carried within the same frequency band or xe2x80x9cchannelxe2x80x9d using different codes. This is possible because only the signal with the correct code ci can be reproduced into the narrowband signal at the targeted receiver. Signals transmitted with other codes ck are not decoded at that particular receiver, and these other transmitted signals will have a noise-like appearance at the receiver. FIG. 2 illustrates this concept.
FIG. 2A represents two independent narrowband signals Sn1 20a and Sn2 22a. These two signals could represent two independent data transmissions, voice transmissions, or the like. Narrowband signal Sn1 20a is transformed using code c1 of the spreading function e(c1), and narrowband signal Sn2 22a is transformed using code c2 of the spreading function e(c2), to respectively produce wideband signals S1 20b and Sw2 22b shown in FIG. 2B. The targeted receiver for original narrowband signal Sn1 20a decodes the signal using the same code c1 to reproduce the narrowband signal Sn1 20c as shown in FIG. 2C. However, because that particular targeted receiver does not include the code c2, signal Sw2 22c is not decoded, and remains a wideband signal Sn2 22c as illustrated in FIG. 2C. The overlapping signal area represented by block 24 represents the noise imparted to the signal Sn1 22c due to the wideband signal Sw2 22c. 
As the number of signal transmissions over the common wideband channel increases (e.g., the number of concurrent users increases), it appears to the reproduced narrowband signal as an increase in background noise. This is illustrated in FIG. 3, which represents the signals seen at a particular signal receiver. As was described in connection with FIG. 2C, the overlapping area 24 is seen by the receiver as noise, so additional signals that are not decoded by that receiver are seen as cumulative noise. For example, FIG. 3 depicts a reproduced narrowband signal Sn1 30, and four other undecoded wideband signals Sw2 32, Sw3 34, Sw4 36, and Sw5 38. Each of the undecoded wideband signals cumulatively increases the noise on the decoded narrowband signal Sn1 32, as illustrated by overlapping noise blocks 40, 42, 44 and 46. Thus, the signal/noise ratio (SNR) of a single user decreases with the increasing number of users or transmitted signals in the common wideband channel. At some limit Nmax, the number of users cannot be increased any more or the individual resulting narrowband signals become too weak. In practice, the users with the weakest signal due to distance and radio conditions are first to lose their radio connection.
In order to guarantee an adequate signal-to-noise ratio (SNR) for existing connections, a control system is required. This would allow a new user to utilize the communication interface only where an adequate SNR would still be available after the new signal has been included in the common wideband frequency channel.
One prior art method of appropriating an acceptable number of users is to count the number of users, and allow new users to be included on the communication interface only if the number of users remains below a predetermined maximum number. In such a case, there is no distinction between users, and all users are treated equally. It is essentially a first-come, first-served system. However, this type of system does not take into account the various needs of different users, and particularly their willingness to pay for a higher degree of certainty that their connection will be made available. Thus, a future third generation network cellular system must be able to differentiate the user desires and needs.
Such a fixed differentiation system may pose complexity problems however. This rigid differentiation scheme does not take into account the magnitude of short term connections that transport relatively short data packets. This type of system would lack efficiency by disallowing many short term transfers, and would inevitably waste available bandwidth capacity.
Therefore, there is a need in the communications industry for a communications control system that allocates radio resources using a dynamically variable priority-based system. Such a system would account for individual users"" willingness to pay more for a higher degree of transmission certainty, or to pay less for noncritical applications. The present invention provides such a system while avoiding the potential complexities and inefficiencies of more rigid schemes. The present invention therefore overcomes the aforementioned and other shortcomings of the prior art, and provides these and additional advantages over the prior art.
The present invention is directed to a system and method for integrating a priority-based quality of service in CDMA communication systems that implement data packet transmission, in order to effectively allocate radio resources.
In accordance with one embodiment of the invention, a method is provided for selectively allocating data packet transfers over a wireless interface operating under a Code Division Multiple Access (CDMA) protocol. A nominal bit rate is established for each user desiring access to the CDMA interface. A relative packet priority is calculated for each of the data packets based on an actual bit rate of the source at the CDMA interface and the established nominal bit rate. An allowable packet priority is calculated for the CDMA interface based on a signal-to-noise ratio of the CDMA interface, and those of the data packets having a relative packet priority greater than or equal to the allowable packet priority of the CDMA interface are transmitted.
In accordance with a more specific embodiment of the invention, a method is provided for selectively allocating data packet transmission over a wireless interface implementing a Code Division Multiple Access (CDMA) protocol, for data packet transmission from a mobile communication unit (MCU) to a trunking network in a centralized implementation. A transmit request signal is transmitted from the MCU to the trunking network via a signalling channel, and the trunking network provides a request response to the MCU indicative of whether the trunking network will permit the data packet to be transmitted. In providing the request response, the trunking network performs a variety of the priority-based functions, including establishing the nominal bit rate for each of the users having access to the CDMA interface, calculating the relative packet priority for each data packet based on an actual bit rate of the sourcing unit at the CDMA interface and the nominal bit rate established for the corresponding one of the users, calculating a current allowable packet priority for the CDMA interface based on a signal-to-noise ratio of the CDMA interface, comparing the relative packet priority for each of the data packets to the current allowable packet priority of the CDMA interface, and setting the request response to indicate whether the data packet has a sufficiently high relative packet priority to gain access to the CDMA interface. The request response from the trunking network is received at the MCU, and the MCU transmits the data packets to the trunking network if the request response indicates that the relative packet priority is sufficiently high to gain access to the CDMA interface.
In such a centralized embodiment, the trunking network calculates a current allowable packet priority for the CDMA interface. In one embodiment, this includes determining the number of users or connections currently occupying the CDMA interface, determining a maximum number of users that are allowed on the CDMA interface such that a predetermined signal-to-noise ratio is not exceeded, calculating the current load condition on the CDMA interface based on a ratio of the number of users occupying the CDMA interface and the maximum number of users allowed on the CDMA interface, partitioning a range of possible load conditions into a range of allowable priority levels, and assigning the allowable priority level corresponding to the calculated current load condition as the current allowable priority level for the CDMA interface.
In accordance with another specific embodiment of the invention, a method is provided for selectively allocating data packet transmission over a wireless interface implementing a Code Division Multiple Access (CDMA) protocol, for data packet transmission from a trunking network to a mobile communication unit (MCU) in a centralized implementation. A nominal bit rate is established for each of a plurality of users having access to the CDMA interface. The trunking network performs a variety of the priority-based functions, including calculating a relative packet priority for each of the data packets based on an actual bit rate at the CDMA interface and the established nominal bit rate, calculating a current allowable packet priority for the CDMA interface based on a signal-to-noise ratio of the CDMA interface, comparing the relative packet priority for each of the data packets to the current allowable packet priority of the CDMA interface, and transmitting the data packets from the trunking network to the MCU if the relative packet priority of the data packets is equal to or greater than the current allowable packet priority of the CDMA interface.
In accordance with another specific embodiment of the invention, a method is provided for selectively allocating data packet transmission over a wireless interface implementing a Code Division Multiple Access (CDMA) protocol, for data packet transmission from a mobile communication unit (MCU) to a trunking network in a distributed, or shared, implementation. A nominal bit rate is established for each user having access to the CDMA interface. The MCU calculates a relative packet priority for each of the data packets based on an actual bit rate provided by the source at the CDMA interface and the nominal bit rate established for the corresponding one of the users. The trunking network calculates a current allowable packet priority for the CDMA interface based on a signal-to-noise ratio of the CDMA interface. The current allowable packet priority is transmitted from the trunking network to the MCU via a signalling channel, and the MCU compares the relative packet priority for each of the data packets to the current allowable packet priority of the CDMA interface. The data packets are transmitted from the MCU to the trunking network if the relative packet priority is equal to or greater than the current allowable packet priority at the CDMA interface.
In accordance with another aspect of the invention, a system is provided for selectively allocating data packet transfers over a wireless interface operating under a Code Division Multiple Access (CDMA) protocol, for data packet transmission between one or mobile communication units (MCU) and a trunking network. The system includes a memory to store a nominal bit rate indicator assigned to each potential connection of the CDMA interface. A bit rate measurement unit receives a data packet that is ready for transmission via the CDMA interface, and measures the bit rate at which the data packet will be transmitted. A packet priority level calculation unit receives the measured bit rate (MBR) and the nominal bit rate (NBR) indicator, and calculates a packet priority level for the data packet in response to the MBR and NBR. A comparator receives the packet priority level and an allowable packet priority level corresponding to the packet priority level required to access the CDMA interface. The comparator compares the packet priority level and the allowable packet priority level, and outputs an enable signal indicative of whether or not the packet priority level is greater than the allowable packet priority level. An output register enables transmission of the data packet when the enable signal indicates that the packet priority level is greater than the allowable packet priority level.